I always thought that the shunt in the bulb had a higher resistance than that of the filament and that an open filament in a bulb would reduce the voltage to the other bulbs in the set.
I've never seen that in any of the bulbs used on sets in Britain. When the filament burns out, the shunt just bridges the contacts directly (Sometimes!
It's quite noticable that the rest of the typical string of 20 lamps are brighter once two or three bulbs have shunted out, and of course the increased voltage can soon result in a chain reaction taking out more bulbs quite quickly.
Sets sold here usually come with one "fuse bulb" (identified by plain glass with just a white-painted tip) intended to open the circuit if too many regular bulbs short out. In practice it quite often takes 5 or 6 to go before the fuse bulb operates.